Abstract In spite of recent advances in the treatment of acute stroke, 20% of chronic stroke survivors suffer from long-lasting language impairments (aphasia). Non-fluent aphasia is one of the most common forms of aphasia, and it is directly associated with social isolation, decreased participation in rehabilitation therapies, and low quality of life. The reestablishment of fluent speech is one of the most challenging aspects during the treatment of subjects with chronic non-fluent aphasia. As a novel alternative to this problem, our group has optimized a new and promising treatment approach entitled speech entrainment therapy (SET), where the subject's speech is pulled along (guided by) an audio-visual model presented on a laptop computer. In a preliminary and proof of concept study, we observed that subjects with non-fluent aphasia could overcome the barrier towards fluency and produce more fluent speech with SET. They had greater than 20% improvement in verbs per minute (VPM) during spontaneous speech at three months after therapy. These are very encouraging findings because they represent sustained post-treatment gains in producing verbs during discourse, which is a valid ecological measure, and a better predictor of language abilities compared with producing nouns or naming objects. Motivated by these findings, we propose a prospective controlled randomized assessor blinded phase II clinical trial entitled Speech entrainment for Aphasia Recovery (SpARc) to better assess the linguistic improvements associated with SET, and to determine the optimal dose of SET. This trial will be a multisite (5 sites) project that will enroll 150 chronically stable stroke survivors with non-fluent aphasia, and the primary outcome will be VPM at 3 months post-therapy. We will use a Seamless Two-Stage Dose Selection design, which will include a Stage 1 to choose the best SET dose, and a Stage 2 to assess the full effects of SET. In Stage 1, the patients will be randomized to 3 different doses of SET: 3 or 4.5 or 6 weeks of 1 hour daily SET, or a control (no treatment) condition (20 patients in each one of the 4 groups). Based on a pre-defined rule, we will select the dose that demonstrated adequate tolerability and was associated the highest group average VPM at 3 months post treatment. In Stage 2, we will enroll 70 additional patients and randomly assign them 1:1 to either the selected SET duration or the control group. The final analysis will test whether the change from baseline in VPM for the selected SET duration group is better than the control group using patients enrolled in Stages 1 and 2. SET will be considered worthy of further study if it leads to an improvement in 20% or more in VPM at 3 months after therapy compared with the no treatment control condition. This study will provide a better understanding of the therapeutic benefits of SET, determine its best dose, and decide whether its effects would justify future studies of this new and promising form of therapy.